Micro-optic ring resonators are attractive for active and passive micro-optical circuits. Rings and discs with directional couplers have generally been realized in lateral and vertical geometries. Coupling of ring resonators with multi-mode interference (MMI) couplers has been demonstrated with ridge-type waveguides on InP. Switching has been demonstrated in active discs using electro-absorption.
It is believed to be desirable to provide devices exhibiting lower losses and good reliabilities.